A turbo-molecular pump used for high-vacuum pumping of a vacuum device such as a semiconductor manufacturing device or a liquid crystal panel manufacturing device includes a plurality of rotor blades and a plurality of stator blades, the rotor blades and the stator blades being alternately arranged. A rotor provided with the rotor blades is, at high speed, rotated relative to the stator blades, and in this manner, gas is exhausted.
When the turbo-molecular pump is attached to, e.g., a vacuum chamber of the semiconductor manufacturing device, a center ring as a seal component might be arranged between a vacuum-chamber-side flange and a suction flange of the turbo-molecular pump (see Patent Literature 1 (JP-A-2014-222044)).
In the case of attaching the turbo-molecular pump to the vacuum chamber, the suction flange and the vacuum-chamber-side flange are joined together after the center ring has been attached to the suction flange of the turbo-molecular pump. The vacuum pump includes the type of attaching the vacuum pump to the vacuum chamber in a portrait orientation, and the type of attaching the vacuum pump to the vacuum chamber in a landscape orientation. In the case of employing the type of attachment in the landscape orientation, the center ring is attached to the suction flange in advance, and then, the vacuum pump is attached to the vacuum chamber with the vacuum pump being tilted. Thus, there is a probability that the center ring is dropped from the suction flange.